I think this will work but I'm not 100% sure. This is really your only option though.

Plug one of these into each if your KRK monitors and run a RCA audio cable to each of them from an audio output on the Aiwa stereo. Example: audio output 1 will have a red and white jack; run the red jack to the right speaker and the white jack to the left.

I'm not sure it will work because these adaptors usually go the other way with the 1/4" jack end being on the output side of things and the RCA's being plugged into the input of something. Like I said though, I think this will work.